This invention is concerned with a technique of providing a wellbore that extends from a surface location of the earth into the earth's crust and passes through a subsurface mineral-bearing formation a plurality of times. More particularly, this invention concerns providing a deviated wellbore which extends along a track in a downwardly direction and penetrates a subsurface mineral-bearing formation from top to bottom. The wellbore is then further deviated and extended along a track in an upwardly direction to again penetrate the formation from bottom to top. This sequence may be repeated to provide further penetrations by the wellbore of the formation.
Wellbores and wells have been extended into the earth in directions other than vertical for various reasons and by various techniques. A need for such wells was early recognized and still exists today for tapping mineral reserves located beneath water bodies or located beneath other poorly accessible surface locations. For example, before the turn of the century the Summerland Field located underwater near Santa Barbara, Calif. was drilled by whipstocking holes out under the water from land locations.
More recent developments have enabled ultrahigh-angle wellbores to be drilled and completed. "Extended reach drilling" is a term that has been coined to describe rotary drilling procedures used to drill wellbores greater than 60.degree. from the vertical and the use of complex wellbore profiles to extend the horizontal limits of wellbores.
In an article entitled "Ultrahigh-Angle Wells Are Technical and Economic Success", THE OIL AND GAS JOURNAL, July 19, 1976, pp. 115-120, there is described a project wherein a well was drilled and completed to 12,300-foot measured depth at an average angle of 82.degree. . In a paper, SPE 6818, "Improved Techniques for Logging High-Angle Wells" by M. W. Bratovitch, W. T. Bell, and K. D. Kaaz, which was presented at the 52nd Fall Technical Conference and Exhibition of the Society of Petroleum Engineers of AIME in Denver, Colo., Oct. 9-12, 1977, it is said that high-angle wells are becoming commonplace, particularly in offshore areas. The paper describes work which contributes to increasing the deviation angles at which wells can be conventionally logged and to deciding whether to try gravity-descent or pump-down tools as a first attempt at logging high-angle wells.
In U.S. Pat. No. 3,285,350 to J. K. Henderson, there is described a technique for drilling off-vertical holes through earth formations and more particularly a technique and apparatus for controllably drilling holes through and substantially parallel to mineral formations between separated wells. A method and apparatus is described for lining wellbores such as bores extending laterally or generally horizontally from a main bore into a surrounding formation in U.S. Pat. No. 2,778,603 to McCune et al.
In U.S. Pat. No. 3,933,447 to Joseph Pasini III et al, there is described a method for the gasification of coal in situ. In one aspect there described, a borehole is drilled from the earth's surface, preferably on a slant so as to intersect the coal bed while traveling in a horizontal direction. Using this technique it was found that major advantages are achieved over the use of vertical wells or blind boreholes. In U.S. Pat. Nos. 3,986,557 and 4,007,788 both to Striegler et al, there are described methods of producing bitumen from subterranean tar sand formations which methods employ a continuous wellbore having a second section thereof contained within the formation and a first and third section extending from said second section to the earth's surface.
A method for removing methane gas from underground coal beds by means of a borehole is described in U.S. Pat. No. 3,934,649 to Joseph Pasini III et al. A borehole is provided that extends through the coal bed in a horizontal direction. In U.S. Pat. No. 4,003,440 to Martin D. Cherrington there is described a method and apparatus for extending a borehole in an inverted arcuate path underneath an obstacle such as a watercourse.
In a copending application U.S. Ser. No. 892,794, filed Apr. 3, 1978, to Joseph U. Messenger, there is described a technique of providing a wellbore that extends from a surface location to a subsurface location spaced a great lateral distance therefrom in a mineral-bearing formation wherein a portion of the wellbore extends a great distance within and essentially parallel to the bedding plane of a formation having good drilling characteristics. The formation having good drilling characteristics may be located above or below the mineral-bearing formation as may be the mineral-bearing formation itself.